By expanding high-purity helium gas at high pressure
through a small cryocooled nozzle
into vacuum, one obtains a supersonic beam of liquid nanodroplets Hen
(n~103-106). These droplets have
sub-Kelvin internal temperatures and are actually superfluid. They are
remarkably efficient at capturing impurity atoms and molecules
in-flight. As a result, they function as transparent, inert, superfluid
"nano-cryostats" for spectroscopy, control of molecular assembly and
reactions, generation of unusual prototype complexes and alloys, etc.